Ceramic pressure sensors comprise a base body and a measurement membrane, wherein the measurement membrane is joined by means of an active brazing solder. A suitable active brazing solder for joining ceramic parts made of corundum is, for example, a Zr—Ni—Ti alloy, since this is compatible with corundum in terms of its coefficient of thermal expansion.
Such an active brazing solder is disclosed in the European patent EP 0 490 807 B1. The European patent document EP 0 558 874 B1 discloses a method for producing rings made of such an active brazing solder; to connect measurement membrane and the base body, rings made of active brazing solder are placed as spacers between the two parts and fused in a high-vacuum brazing process, whereby a pressure-sealed and high-strength annular connection is created between the two ceramic parts. An alternative to the application of solder in the form of pre-manufactured rings is to provide the active brazing solder in a screen printing process. A paste of active brazing solder that is capable of being screen-printed, and a method for its production, are disclosed in the European patent document EP 0 988 919 A1.
However, the rings can only be produced in reproducible quality at a minimum thickness of approximately 30 μm, and the screen-printable paste also has grains, which lead as a result to joining regions having a minimum thickness of approximately 30 μm between the ceramic parts.
The need for a thinner joining region follows indirectly from the desire for miniaturization of pressure sensors, since—for example, given a ceramic pressure sensor having a capacitive transducer—the miniaturization leads to a reduction in size of the electrode surfaces of the capacitive transducer, which then is to be compensated for by a reduction of the clearance.
The disclosure document DE 10 2010 043 119 A1 discloses a method for producing a connection between two surfaces or surface segments of two ceramic parts, in which the entirety of the active brazing solder material is provided for connecting the first and second ceramic parts in such a manner that a surface segment of one or both ceramic parts is layered with the alloy of the active brazing solder and/or its components by means of a chemical vapor deposition. The chemical vapor deposition may thereby take place by means of sputtering or cathode sputtering, for example. The sputter target (which contains the alloy of the active brazing solder in the desired composition) may be produced by means of powder metallurgy, for example. However, the powder metallurgy production of such a target is complicated, especially when the targets contain active components. This then requires size reduction and powdering processes in a hydrogen atmosphere.